Transponders are electronic devices of small size and low cost which can be placed on objects or in a very wide variety of locations for the purpose of transmitting in predetermined form data which have been programmed in their respective memories, whenever they are subjected to external radiation having predetermined characteristics, e.g. electromagnetic radiation.
In general, such transponders do not have their own electrical power supplies, and the energy required for transmitting the data they contain is a result of the fact that the radiation sent to them and picked up by them is used, for example, to charge a capacitor which then delivers its energy to an electronic circuit of the transponder to enable it to perform the transmission that serves as a medium for the data it sends.
The responses provided by the transponders, after they have been subjected to the action of external radiation that triggers their operation, are governed by rules of a specific protocol which determines successive time intervals (or transmission windows) during which a transponder transmits the radiation which conveys the data contained in its memory, and successive time intervals (or reception windows) during which a transponder does not transmit, but during which it is capable of receiving data transmitted in the form of radiation coming from an external transmitter. This latter data can then be stored in the transponder.
It will be understood that in order to perform its function, a transponder must be associated with an external transmitter/receiver whose characteristics are such that firstly it is capable of transmitting radiation that will supply the transponder with the energy it needs, and secondly that it can receive and understand data transmitted by the transponder in its transmission windows, and can also transmit data that the transponder can receive and understand in its reception windows.
The simplest and cheapest transponders are said to be "read-only" since they cannot be programmed to record new data and are capable only of transmitting unchanged data contained in memory.
Higher performance and slightly more expensive transponders are said to be "read/write" transponders and they can receive data from the external transmitter and store it in memory for subsequent retransmission when interrogated.
Such data writable in the memory of a transponder of this type can be modified at will with the help of the external transmitter.
In a variant of this second category, transponders that are said to be "respond-to-order" transponders transmit to the external receiver only when the external transmitter instructs them so to do, thereby enabling them to be synchronized by sending the same order simultaneously to all of the transponders.
A further improved, third category of transponders is said to be "addressable", in which the transponders can be interrogated and programmed individually even when they are grouped together, however such transponders are significantly more expensive than those of the preceding category.
Transponders are presently in use in very large numbers in many fields, in particular during manufacture for the purpose of identifying objects at various stages of manufacture.
They are used in particular when manufacturing garments or other textile products to identify a large number of garment parts during manufacture, or once manufactured, what parts are contained in a common container, each part including a transponder that needs to store in its memory various kinds of data concerning the garment.
Thus, during garment manufacture, the transponder of the garment must contain in its memory a first data group concerning the type of garment, the kind and color of the fabric, and also the size.
Garments are generally manufactured in series of identical garments which are grouped together in a common container, and it is necessary to inject this first data group into the respective memories of the transponders in this series of garments.
For shipping to customers, the garments manufactured in this way are then distributed in various different containers, each capable of receiving garments of different types, different colors, and different sizes, thereby making it necessary to inject into each of the transponders a second data group concerning the identity of the customer and shipping conditions, naturally while making no changes to the data in the first group concerning, for example, the size and the color of the fabric.
In the state of the art, such programming of the various transponders associated with each garment is an operation that is difficult and expensive.
When read/write transponders are used, it is not possible to program them all simultaneously, since the transmitter will not, as a general rule, recognize them as constituting a single transponder given that the transmitter is incapable of reading simultaneously the identity signals from all of the transponders, because the signals are not synchronized.
When using addressable transponders of much higher cost, the transmitter can address each transponder individually to program in its memory the data that is to be inserted therein. However, inserting the data group into all of the articles takes a considerable length of time since it is necessary to interrogate and program in succession each of the transponders in the batch that is to be programmed.